Pak1 as a novel therapeutic target for antihypertrophic treatment in the heart.

BACKGROUND: Stress-induced hypertrophic remodeling is a critical pathogenetic process leading to heart failure. Although many signal transduction cascades are demonstrated as important regulators to facilitate the induction of cardiac hypertrophy, the signaling pathways for suppressing hypertrophic remodeling remain largely unexplored. In this study, we identified p21-activated kinase 1 (Pak1) as a novel signaling regulator that antagonizes cardiac hypertrophy. METHODS AND RESULTS: Hypertrophic stress applied to primary neonatal rat cardiomyocytes (NRCMs) or murine hearts caused the activation of Pak1. Analysis of NRCMs expressing constitutively active Pak1 or in which Pak1 was silenced disclosed that Pak1 played an antihypertrophic role. To investigate the in vivo role of Pak1 in the heart, we generated mice with a cardiomyocyte-specific deletion of Pak1 (Pak1(cko)). When subjected to 2 weeks of pressure overload, Pak1(cko) mice developed greater cardiac hypertrophy with attendant blunting of JNK activation compared with controls, and these knockout mice underwent the transition into heart failure when prolonged stress was applied. Chronic angiotensin II infusion also caused increased cardiac hypertrophy in Pak1(cko) mice. Moreover, we discovered that the Pak1 activator FTY720, a sphingosine-like analog, was able to prevent pressure overload-induced hypertrophy in wild-type mice without compromising their cardiac functions. Meanwhile, FTY720 failed to exert such an effect on Pak1(cko) mice, suggesting that the antihypertrophic effect of FTY720 likely acts through Pak1 activation. CONCLUSIONS: These results, for the first time, establish Pak1 as a novel antihypertrophic regulator and suggest that it may be a potential therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Mutation-specific effects of polymorphism H558R in SCN5A-related sick sinus syndrome.

INTRODUCTION: Mutations in SCN5A, the gene encoding alpha subunit of cardiac type sodium channel, Na(v)1.5, lead to familial sick sinus syndrome (SSS). Although several molecular mechanisms for this genetic condition have been explored, the underlying mechanisms for the variable genotype-phenotype relationships have not been well addressed. One of the important contributors to such relationships is the genetic background such as single-nucleotide polymorphisms. METHODS AND RESULTS: To clarify the effects of a common polymorphism in SCN5A gene, H558R, on SCN5A-related SSS phenotype, we investigated the electrophysiological properties of all of the 13 known SSS-related hNa(v)1.5 mutant channels on both H558 and R558 background. Electrophysiological properties of hNa(v)1.5 mutant channels were investigated by the whole-cell patch clamp technique in HEK293 cells. When peak currents were affected by the mutation, cell surface biotinylation was performed to quantify the fraction of correctly cell membrane-targeted mutant channels. Loss-of-function defect of D1275N in SCN5A was rescued by R558 through enhancing cell surface targeting and improving steady-state activation of the mutant channels. In contrast, the defects of mutants E161K, P1298L, and R1632H were aggravated in the R558 background, mainly due to the reduced steady-state availability of mutant channels. The electrophysiological properties of the remaining SSS-related hNa(v)1.5 mutants including the missense mutants (L212P, T220I, DelF1617, T187I, R878C, G1408R), and the truncated mutants (W1421X, K1578fs/52, R1623X) were not significantly affected by H558R. CONCLUSION: We conclude that polymorphism H558R has mutation-specific effects on SCN5A-related SSS. Our data highlight the importance of common genetic variants in modulating phenotypes of genetic diseases.

Thyroid and Cardiovascular Disease: A Focused Review on the Impact of Hyperthyroidism in Heart Failure.

The association between thyroid hormones and cardiovascular conditions has been well studied, specifically, the effects of hypothyroidism on cardiomyopathy, and hyperthyroidism with arrhythmias. Nonetheless, an explicit correlation between hyperthyroidism and cardiomyopathy has yet to be established. Medical databases MEDLINE and PubMed were accessed and queried as primary sources for data acquisition. Search criteria consisted of "hyperthyroidism", "heart failure", and "thyroid and cardiovascular system", which allowed the retrieval of relevant and recent works. From these sources, a consensus was developed and employed to yield an updated review of the etiology of heart failure in the setting of hyperthyroidism. It is rare for patients with hyperthyroidism to remain in a chronic hyperthyroid state, making it difficult to analyze subsequent long-term effects on the cardiovascular system. Related to heart failure, some studies have demonstrated no change in ejection fraction, while others have shown an acute change along with diastolic dysfunction, with or without an underlying rhythm abnormality. Further investigation is warranted to elucidate the mechanism driving such cardiac dysfunction, and whether it is due to vascular changes, tachyarrhythmias, or myocyte remodeling and fibrosis. The intent of this review article is to improve our understanding of how a hyperthyroid state affects cardiovascular function. An enhanced understanding of the effects on cardiovascular physiology will afford physicians the ability to provide more comprehensive care in consideration of both endocrine and cardiovascular pathologies.

Prior beta blockers use is independently associated with increased inpatient mortality in patients presenting with acute myocardial infarction.

BACKGROUND: Beta blockers (BBs) are recommended for patients presenting with acute myocardial infarction. However, the effects of prior BBs use on inpatient mortality in patients presenting with acute myocardial infarction (AMI) are unknown. METHODS: This was a retrospective cohort study of patients presenting with AMI in Florida Hospital Orlando from January 1, 2013 to December 31, 2014. Data were collected prospectively, as part of the Acute Coronary Treatment and Intervention Outcomes Network (ACTION) Registry. RESULTS: 1128 patients were included in the analysis, with 354 (31.4%) patients on home BBs and 774 (68.6%) not on home BBs on presentation. Patients in prior BBs group were older, had higher incidence of multiple comorbidities, and were more likely to take cardiovascular medications. During hospitalization, Patients in prior BBs group were more likely to develop decompensated heart failure (9.9% vs. 3.6%, P<0.001), less likely to have STEMI (33.9% vs. 54.4%, P<0.001), and subsequently less PCI (73.2% vs. 81.3%, P=0.002), but higher inpatient mortality (8.8% vs. 4.8%, P=0.009). In multivariable logistic regression analysis, prior BBs use was independently associated with increased inpatient mortality (adjusted OR 3.15, 95% CI 1.44-6.87, P=0.004), as well as in GRACE model (adjusted ratio=1.83, 95% CI 1.01-3.34, P<0.047). However, prior BBs use did not contribute significantly to predict inpatient mortality on the basis of GRACE model in terms of discrimination and calibration. CONCLUSIONS: Prior BBs use was independently associated with increased inpatient mortality, and should be considered a high risk marker for patients presenting with acute myocardial infarction.

Kansas City Cardiomyopathy Questionnaire Utility in Prediction of 30-Day Readmission Rate in Patients with Chronic Heart Failure.

Background. Heart failure (HF) is one of the most common diagnoses associated with hospital readmission. We designed this prospective study to evaluate whether Kansas City Cardiomyopathy Questionnaire (KCCQ) score is associated with 30-day readmission in patients hospitalized with decompensated HF. Methods and Results. We enrolled 240 patients who met the study criteria. Forty-eight (20%) patients were readmitted for decompensated HF within thirty days of hospital discharge, and 192 (80%) patients were not readmitted. Compared to readmitted patients, nonreadmitted patients had a higher average KCCQ score (40.8 versus 32.6, P = 0.019) before discharge. Multivariate analyses showed that a high KCCQ score was associated with low HF readmission rate (adjusted OR = 0.566, P = 0.022). The c-statistic for the base model (age + gender) was 0.617. The combination of home medication and lab tests on the base model resulted in an integrated discrimination improvement (IDI) increase of 3.9%. On that basis, the KCQQ further increased IDI of 2.7%. Conclusions. The KCCQ score determined before hospital discharge was significantly associated with 30-day readmission rate in patients with HF, which may provide a clinically useful measure and could significantly improve readmission prediction reliability when combined with other clinical components.

A tarantula-venom peptide antagonizes the TRPA1 nociceptor ion channel by binding to the S1-S4 gating domain.

BACKGROUND: The venoms of predators have been an excellent source of diverse highly specific peptides targeting ion channels. Here we describe the first known peptide antagonist of the nociceptor ion channel transient receptor potential ankyrin 1 (TRPA1). RESULTS: We constructed a recombinant cDNA library encoding ∼100 diverse GPI-anchored peptide toxins (t-toxins) derived from spider venoms and screened this library by coexpression in Xenopus oocytes with TRPA1. This screen resulted in identification of protoxin-I (ProTx-I), a 35-residue peptide from the venom of the Peruvian green-velvet tarantula, Thrixopelma pruriens, as the first known high-affinity peptide TRPA1 antagonist. ProTx-I was previously identified as an antagonist of voltage-gated sodium (NaV) channels. We constructed a t-toxin library of ProTx-I alanine-scanning mutants and screened this library against NaV1.2 and TRPA1. This revealed distinct partially overlapping surfaces of ProTx-I by which it binds to these two ion channels. Importantly, this mutagenesis yielded two novel ProTx-I variants that are only active against either TRPA1or NaV1.2. By testing its activity against chimeric channels, we identified the extracellular loops of the TRPA1 S1-S4 gating domain as the ProTx-I binding site. CONCLUSIONS: These studies establish our approach, which we term "toxineering," as a generally applicable method for isolation of novel ion channel modifiers and design of ion channel modifiers with altered specificity. They also suggest that ProTx-I will be a valuable pharmacological reagent for addressing biophysical mechanisms of TRPA1 gating and the physiology of TRPA1 function in nociceptors, as well as for potential clinical application in the context of pain and inflammation.

Tracing the evolution of the mitochondrial protein import machinery.

Mitochondria are eukaryotic organelles originated from a single bacterial endosymbiosis about 2 billion years ago. One of the earliest events in the evolution of mitochondria was the acquisition of a mechanism that facilitated the import of proteins from cytosol. The mitochondrial protein import machinery consists of dozens of subunits, and they are of modular design. However, to date, it is not clear when certain component was added to the machinery. Using extensive homology searches, the evolutionary history of the mitochondrial protein import machinery was reconstructed. The results indicated that 6 of the 35 subunits have homologs in prokaryote, suggesting that they were prokaryotic origin; the major subunit gains were occurred in the earliest stage of eukaryotic evolution; subsequent to the gain of these conserved set of subunits, the mitochondrial protein import machinery components diversified along the eukaryotic lineages and a number of lineage-specific subunits can be observed. Furthermore, protein import systems of mitochondria-like organelles (hydrogenosomes and mitosomes) have dramatically reduced their subunit contents, however, they share most of the prokaryotic origin components with mitochondrion.

Multiple loss-of-function mechanisms contribute to SCN5A-related familial sick sinus syndrome.

BACKGROUND: To identify molecular mechanisms underlying SCN5A-related sick sinus syndrome (SSS), a rare type of SSS, in parallel experiments we elucidated the electrophysiological properties and the cell surface localization of thirteen human Na(v)1.5 (hNa(v)1.5) mutant channels previously linked to this disease. METHODOLOGY/PRINCIPAL FINDINGS: Mutant hNa(v)1.5 channels expressed by HEK293 cells and Xenopus oocytes were investigated by whole-cell patch clamp and two-microelectrode voltage clamp, respectively. HEK293 cell surface biotinylation experiments quantified the fraction of correctly targeted channel proteins. Our data suggested three distinct mutant channel subtypes: Group 1 mutants (L212P, P1298L, DelF1617, R1632H) gave peak current densities and cell surface targeting indistinguishable from wild-type hNa(v)1.5. Loss-of-function of these mutants resulted from altered channel kinetics, including a negative shift of steady-state inactivation and a reduced voltage dependency of open-state inactivation. Group 2 mutants (E161K, T220I, D1275N) gave significantly reduced whole-cell currents due to impaired cell surface localization (D1275N), altered channel properties at unchanged cell surface localization (T220I), or a combination of both (E161K). Group 3 mutant channels were non-functional, due to an almost complete lack of protein at the plasma membrane (T187I, W1421X, K1578fs/52, R1623X) or a probable gating/permeation defect with normal surface localisation (R878C, G1408R). CONCLUSIONS/SIGNIFICANCE: This study indicates that multiple molecular mechanisms, including gating abnormalities, trafficking defects, or a combination of both, are responsible for SCN5A-related familial SSS.